Are you running any sort of a heat shield beneath the carb/manifold or just the carb?
Right now just the carb, no heat shield. I didn't have a big problem with my duals and the exhaust heat, and there is a TON more room for airflow back there now with just the single. Did a bit more filing to the exhaust manifold, and remade the special bolt I had to make to bolt this facker up. It fits quite well now .
Oh yeah...it runs too .
I can't really comment on the throttle response, because I'm running the mixture screws at 7 turns out (starting position is 1 turn out according to the Mikuni manual), so I need WAY bigger idles. Ignoring the slight lean bog, it revs up SUPER fast...almost faster than the duals did. If I can rig up the throttle cable, I'll have a better idea of the jets I'll need, right now here's the specs:
-32 chokes (I love low end grunt, plus...mikuni parts aren't exactly growing on trees anymore. I'll have the spare two 32s machined out to 34s if I have to)
-1.5 needle (have a 1.8 in case I need to up the fuel flow to the bowls)
-4psi fuel pressure (seems to run well at this, like my dells did)
-7 turns out on the mixture screws
Quote, originally posted by vwbeaner » I have been following this thread for a while and I think there is more info here than on the FAQs page, Keep up the good work
I'm glad it's becoming useful to folks out there . I learned a lot from that FAQ, and just want to share my experiences as a repayment of favor to the forum. I have to say a big thanks to the12for12...I followed most of his posts for years before I jumped into the carb pool .
I've got the 'rush' again...just like with the first startup of the duals, I want to go back to the garage to hear the car run .
Throttle cable done...but I'm not going to put up pics just yet. After spending a few hours fabbing it up to work exactly perfect...I realised that it was kludgey and ugly looking . Works PHENOMENALLY well, and is simple...but it's hideous and overpowering when you look in the bay. Not really what I wanted. I've got another idea in my head though, just need to round up a few bits and pieces .
Started fabbing up a throttle cable bracket the other day. Ended up with this monstrosity, which worked GREAT but looked like hell. It fouled the hood, and generally overpowered the bay...which wasn't what I was after.
Needless to say, I took that one off today and started to work on a new one. Turns out I didn't have to work too long either. In the box of spare carb parts that I have, I found a ready-made cable bracket! Talk about powers of observation . The only issue is that my bracket was made to work with the stock MkI-style cable, and the new bracket needed a hybrid cable made out of a spare junk universal cable that was in the parts bin, and a MkII one. I have to order a cable end, but Lokar makes a sweet one, so no biggie .
A buddy who runs dual Mikunis on his racecar has kindly loaned me this box of magic fueling devices to sort out the tuning .
Modified by B4S at 9:49 PM 9-18-2008
I love it!
Keep them coming!
Very nice, how does it run? Probably a hoot .
Cable end, done. Even though the end product is far from a CAD-designed piece. Cut a 1" piece of square bar (more or less), drill a small, cable-sized hole down the top, about half way through (lengthwise). Drill a slightly larger hole in one of the sides for the pinch bolt. Tap that hole (and weld a nut on it, for extra holding force). Flip it over and drill a large-ish hole (didn't measure) for the ball end. Done .
I have to figure out a way to keep the holder on the ball end, but that's cake.
A crappy Paint drawing...because it's better looking than the real thing .
Great idea...but didn't work out . Too many issues, and was a bit too custom for my current requirements. I swapped back to my original too-big bracket that used the OE cable. Works much better .
So far I'm up to:
-160 mains (a bit too small, gonna try 162.5s)
-180 airs (trying 170s tomorrow, leans out too far at top end)
-60 idles (need to bump to 65-70, the throttle screws are still 3.5 turns out and the transition between cruise and WOT is horrible)
-50 pumps (need at least 60s, but I'm going to try increasing the pump stroke tomorrow and see if it helps at all. It's tough to tune this part until I get the idle jets sized up correctly).
All in all, it's driveable, if a bit richer (14:1) under cruise conditions than the Dellortos. It's faster and louder, which is interesting, because I never figured on the intake noise.
The mikunis have a fixed idle air, like the emissions Dells I had before. It's 1.4mm in diameter vs. the 2.2mm on the Dells. It is a 4-progression hole carb, and according to the Mikuni manual, one turn out on the mix screws is where I should be-ish. I'm 3-3.5 turns out, so it idles at 13:1 just great, but the minute it needs to get deep into the progression phase it goes off the scale lean until I get the throttle past the ports and unshroud the mains. If I slow down in top gear, to about 1200 rpm, and go WOT it goes 12:1, then off-the-scale-lean, then picks up again around 1500-1700. At least I know the mains aren't coming in late, especially not with 170 airs, lol.
WOT right now is great (12.6:1 - 13.5:1) until around 4500, where it starts to hit 14:1. I am still running a 1.5 needle, but have a 1.8 to install if I think it needs it. I'm reserving judgement on that until I get the transition dialed in. Ultimately, I think with the proper idle jetting, I'll be able to go to a 170 main and 200 air, to get the top end back without relying on the partially shrouded main to provide fuel under cruise conditions.
Modified by B4S at 12:05 PM 9-21-2008
I re-tested, just for my own anal retentiveness. It's definitely idle jet related, I've confirmed that. I went for a drive and verrrrrrrrrrrrrry slowly tried to accelerate from a stop. As soon as the throttle plate hits the ports, it goes off the scale lean. If I pedal through it, the mains kick in, and VROOM.
I ordered some 65 and 67.5 idles (up from my current 60), and hopefully they'll be in next week so I can get back to tuning the car. It sucks that the local bike shops can't get any richer idles than 60, I had to order from eBay.
Next week, I'll try the richer idles, and play with the airs a bit. I think it's super close to being correct.
Whoot! Got it 95% perfect .
Bumped the mains up to 167.5, airs to 180, and it's almost bang on.
Only one minor issue. At 5000 in third (long ratio 4 speed), it seems to run out of fuel. I'm using 32mm chokes, and it goes off the scale lean at that point. Think it could be a too-small needle valve? I'm running a 1.8 in it now, with 4psi of fuel pressure. Or is it the chokes maxing out?
Modified by B4S at 4:30 PM 9-25-2008
It's not that there is nothing left, it's that the car starts to buck like I'm bouncing off the rev limiter, lol. The wideband is off the scale lean while it's happening too. In 1st and 2nd, it revs way up above 5000, but in third it goes nuts at that point. It's definitely load related, just not sure if it is because I'm out of fuel or not.
Went out to do a bit more tinkering, to see if I had made a newb mistake. Turns out I did, although it didn't really fix the problem. I had installed the 1.8 needle, but didn't reset the float level. It was 2-3mm too low, so I fixed that up right away and took it for a spin. It still 'bounced' off an invisible ceiling, but it was 5200 rpm now, and not as violent. It's definitely chokes, since that's a massive change in float level, and surely it would have made some difference in the fueling up top if that had been the issue. It hauls ASS past 6 grand in 2nd gear, if I didn't shift it would be past 7000 in the blink of an eye...but the minute it starts to get some real load, doh .
Made myself a 2.0 needle today, up from the 1.8 that was in it. It made a bit of a difference, but the rest of the testing DEFINITELY pointed to it being a fuel issue. In third, WOT, it would die at 5200-ish, then a shift into 4th had it staying at 3000 and doing the same thing. If I went WOT in fourth from 3000, it EVENTUALLY got to 4000, and started bucking. The chokes are certainly too small for a top end setup in my car, I can feel it flattening out, but the real issue is the needle valve. The biggest that I can get is a 2.0, and my first attempt at a 2.25 failed because the needle itself doesn't seat far enough into the opening due to its design. Looks like before next spring, I'm going to have to swap to one of my Dells 40s(with a 2.25-2.5 needle) and 34-36mm chokes, or get lucky on ebay and find a Dellorto 45 (have too many parts for these carbs to justify swapping to a Weber 45). For now, it drives great, so I'm just gonna leave it alone .
Speedo stopped working today, so while I was playing around in the garage, avoiding pulling the cluster, I started poking at the Dells. The throttle shaft felt great, no wobble, no play, I was stumped until I checked the cold-start choke mechanism. It wasn't closing all the way, and it looked like someone had McGuyvered it when it was rebuilt. It would barely seal at the top of the tubes to feed the cylinders, and the air ports would stay open ever so slightly. This could explain why the mixture screws didn't have as much impact on the running of the car as the ones on the other carb did. I've further McGuyvered it, with some high temp copper gasket goop, since it's only the air ports that are exposed a bit, the fuel ports are further up the bore. Basically just plugged the air intake holes .
I'm going to get a straight-edge and test the manifold for warpage next....oh yeah, and fix the speedo.
Here's how the last couple weeks have gone...hell of a rollercoaster IMO.
-traded the mikunis away.
-set up a Dellorto as a single.
-ordered jets and larger needle valves.
-swapped out suspected bad fuel pump, swapped in known good one.
-installed new jets and biggest needle possible.
-take car for test drive, end up getting stranded about a km outside of town. Push car half way, get lift to house, tow rabbit home with Saturn. Did I mention this was after the sun went down?
-discover fuel filter was completely clogged, so no fuel was going to carb.
-realise mikuni could have worked, and suspected dead pump wasn't dead at all, feel stupid.
-soldier on with the tuning, get it pretty much bang on.
-feel huge relief, because now I can drive my car again
I'm running a 1.75 needle, and with the clogged filter removed, all trace of high rpm hesitation is gone. I need to get some smaller airs to get it perfect, but right now, it's pretty darn close .
-65 idles (could probably go to 60s to regain the lost mega-fuel economy, since it now cruises at 14:1 instead of 16:1)
-42 pumps (way too small, but not going to order new ones until spring).
Modified by B4S at 10:20 PM 10-9-2008
Not according to my wideband .
I'm sure that I could run a smaller main and air, and get even better results. I was originally testing a 180 main and 200 air, with nearly the same results (even a bit leaner), and by going to the 165 main with a 170 air, I've actually gotten richer at WOT below 4500. Ideally I think I need a 160 main with a 160 air to nail it perfectly...but it's also starting to get colder here, so I'll leave it where it is until I can do some warmer weather testing.
As for why the single...well, I guess I just like it . It's something that there isn't much info about out there, and to be honest the duals were too much for my setup. It's so much quicker with the single, I'd have to go to 30mm chokes or smaller to get the same effect with the duals. Ultimately, I'm running carbs to learn more about tuning, and the single is definitely a learning experience.
Dropped my idles down to 60, with the 165 mains and 170 airs. Now I've regained my fuel economy (according to the wideband anyway), and still have the AFRs I want up top. The flat spot in transition is a bit worse now (obviously), since I need to get way bigger pumps, but the guy I deal with won't have any until spring...and he's half the price of anywhere else.
Might as well add a pic...everyone loves pics .
Quote, originally posted by idrivemyself » YAY PICTURES!!! (Applaudes wildly )
Edit: Whats with the dual coil setup? The RedBull can on the firewall... Have you also thought about tapping the 2-3 runner for vacuum to even the manifold out?
Modified by idrivemyself at 11:42 PM 10-13-2008
The Jacob's ignition I'm using uses the stock ignition setup to trigger itself. I could have wired it in right off the ICM, but have heard so many things over the years about aftermarket ignitions leaving people stranded that I felt I wanted a backup plan. This way, if the Jacobs stuff kicks it, all I need is a stock coil wire and I'm back up and running .
Quote, originally posted by impulse byer »
Yes they do Out blowing some leaves off the roads today. Drove it last week some mornings starting in 3C(36F?) temps was fun
Modified by impulse byer at 5:51 PM 10-13-2008
Dude, nice shot! Red rocco + red trees =